1. Field of the Invention
The present invention relates to a working apparatus, and, in particular, it relates to a system for supplying an illuminating laser beam to an exposing apparatus for manufacturing semi-conductor integrated circuits.
2. Related Background Art
In general, exposing apparatuses for manufacturing semi-conductor IC or LSI have been proposed in such a manner that each of the exposing apparatuses included a light source for providing exposure energy. Further, in order to reduce weight of the system, it has been proposed that a single source of laser beam was used in common with respect to a plurality of exposing apparatuses so as to selectively supply exposure energy to a desired exposing apparatus from the single laser beam source, as described in U.S. Pat. No. 4,653,903.
Nowadays, ultraviolet rays such as g-ray (having a wavelength of 436 nm) or i-ray (having a wavelength of 365 nm) emitted from a mercury lamp have generally been used as a light source for exposure energy. Recently, pulse generating laser, and particularly excimer laser having a strong spectrum in the ultraviolet band or zone and having strong output intensity has been remarked.
In the excimer laser apparatus, laser is generated by applying discharge energy to a laser medium comprising the mixture of halogen and rare gas. Therefore, the use of the excimer laser apparatus requires installations for supplying a gas such as halogen at high pressure and for generating a high voltage required for a discharge phenomenon.
Accordingly, the excimer laser apparatus will be of a large size as a whole since it includes such installations as well as a plurality of pipes for the used gases. Further, in the excimer laser apparatus, since the poisonous or toxic gases are used, security regarding such toxic gases must be considered and maintained. Furthermore, in the excimer laser apparatus, noise due to the discharge is apt to exert a bad influence upon peripheral equipments, and there arises dust during operation and/or maintenance of the laser apparatus.
On the other hand, since a clean room in which the exposure operation is performed is very expensive in the cost of its construction, as interior space thereof must be utilized effectively. Further, since the clean room is a closed room, security thereof must be maintained; and, since in the clean room many precision machines sensitive to the noise are normally settled and are in operation, a measure to counter the noise must be considered. In addition, since the clean room is naturally prejudiced against the dust, apparatuses or machines which generate the dust should not be installed in the clean room to the utmost.
For these reasons, when the excimer laser apparatus is installed in the clean room, there arise many problems such that a large space is occupied by the laser apparatus; that another danger due to the laser apparatus will occur; that the noise and/or dust are generated by the laser apparatus; and that the maintenance of the laser apparatus will be difficult, and the like.
Further, when the pulse generating laser created on the basis of the gaseous laser medium is used, since the number of luminous pulses is limited due to deterioration of the laser medium, the laser medium must be replaced periodically. Further, since window plates provided on a laser discharging chamber are soiled or stained by a halide and the like, these window plates must be replaced periodically.
In the prior art mentioned above, there was a problem that when the operation of the laser source is stopped due to trouble or maintenance the whole exposing apparatus is also stopped.